Document v6OBYkKZyemKMeB1E5gdqaK4Z

672 CHAPTER 49 1959 Guide Table 1.... Data for Determining Operating Characteristics of Snow-Melting Systems*'1 Period of Ho Saewfafl Period of SnowfafP Air Temperature, P Hours of snowfall* Car Mow Over 32 or equal Wind < to 32 % of winter boor* with no freezing period* period,* mph Per- Hr Pr year J} a a snow at above temperature* 1 Albuquerque, N. M......... 74.7 Amarillo, Tex.................... 73.1 Boston, Mass..................... 64.6 24.7 26.0 31.4 26.2 24.6 24.7 8.5 0.6 22 fl 10 13.3 0.9 33 /l to 14.2 145 \0 Buffalo \vr v Niagara Falla/ ............... Burlington, Vt.................. Caribou \w Limestone/"1*................... 46.5 39.0 21.4 46.9 54.5 70.6 23.9 19.6 16.5 10.8 240 to 10.8 10.0 6.5 236 8.0 290 /l /Ifl) \o Required output, Stu per (sq ft) (hr)* Maxi mum to to to to0 to 49 50 99 too 149 150 to 199 200 249 250 to 299 300 349 350 to 399 400up output, Btu/ (sq ft) 0w> Frequency distribution of tnowfaD hours at above outputs, percent* =62.0 25.4 7.6 4.2 0.0 0.8 - - 94.1 5.9 259 82 33.7 35-4 15.4 10.7 3.0 1.8 " -- 260 88.1 10.1 1.8 143 1.2 320 83.2 14.0 2.0 0.3 0.3 0.1 0.2 " 370* 50.7 3.7 1.4 0.2 _ _ 309 95.9 3.4 0.2 0.5 53-7 29.9 13.2 2.5 0.6 0.1 -- _ 192 280 91.8 7.6 0.6 142 35.0 39.7 16.0 5.7 2.0 1.0 0.5 0.1 -- 378 92.0 7.5 0.5 138 Cheyenne, Wyo................. 46.4 Chicago, HI....................... 45.4 Colorado Springs, Colo... 54.3 49.8 50.9 43.6 21.5 21.4 22.1 15.3 11.5 11.5 3.8 138 3.7 134 2.1 76 fl tho t/oi to 16.5 94.3 45.8 91.5 26.8 98.4 26.2 19.4 13.1 8.6 5.4 0,3 37.4 11.4 3.1 .1.4 8.1 0.3 0.1 36.3 19.0 7.5 4.4 .1.6 4.7 4.2 4.7 2.6 499 129 0.6 0.2 0.1 368 165 5.5 0.5 -- -- 311 63 Columbus, Ohio............... 59.0 Detroit, Mich.................... 47.0 Duluth, Minn.................... 12.6 38.1 49.3 80.5 24.5 24.1 14.5 10.0 10.6 12.0 2.9 105 3.7 134 6.9 250 /i to h t/oi to 65.8 97.7 60.4 95.9 23.7 94.8 22.4 8.0 1.7 2.3 27.7 9.3 1.5 3.5 0.6 32.9 20.6 13.7 4.7 0.0 0.3 1.7 0.8 4.3 0.2 0.4 = = = 0.3 -- 2.5 1.7 0.6 261 72 278 140 382 206 - Falmouth, Mass................ 68.5 Great Falls, Mont............ 49.0 Hartford, Conn................. 66.4 29.5 46.2 38.9 25.5 16.5 24.4 Linooln, Neb..................... 45.0 Memphis, Tenn................. 87.2 Msti.npneoaTpolis1"!..TM' ............ 23.6 52.5 12.5 70.8 20.8 27.0 12.8 2.0 73 fi to 50.0 91.5 33.9 14.2 7.4 1.1 1.6 0.3 - - r; - 204 144 14.4 4.8 174 h to 26.2 94.6 27.6 16.7 16.4 4.8 0.6 7.5 4.6 0.3 0.5 0.2 451 138 8.2 4.7 171 h to 48.4 80.4 34.6 11.2 16.7 2.2 4.3 0.8 0.5 0.7 -- 0.1 0.1 0.1 .396 383 10.1 . 2.5 91 to 97.2 20.0 13.9 5.7 2.6 0.0 0.0 0.2 _ __ _ 293 -- -- -- 202 11.5 0.3 11 to 85 0 13.3 8.3 6.7 227 144 11.1 5.6 203 to 28.4 96.5 31.4 21.7 14.1 3.1 0.3 0.1 3.5 0.6 0.2 -- -- 313 155 Mt. Home, Idaho............. 56.3 New York, N. Y............... 55.7 Ogden, Utah...................... 50.0 42.6 42.2 45.6 24.9 24.3 9.5 1.1 40 ri to 74.2 98.1 21.9 1.9 3.9 143 90 11.8 76 to 87.6 1.6 0.2 385 9.6 1 5 0.7 0.3 0.3 -- -- 298 160 to 88.8 0.1 216 9.4 1.4 0.3 0.1 - - - - 216* Oklahoma City, Okla. .,.. 79.0 Philadelphia, Pa............ 75.8 Pittsburgh, Pa.................. 55.2 19.8 22i6 39.8 24.6 24.3 15.8 1.2 1.6 44 /i to to 27.8 95.7 84.3 18.7 17.0 12.6 14.3 4.3 2.3 0.9 14.0 1.1 0.2 0.4 5.9 2.7 1.0 " ------ 394 81 296 229 11.6 5.0 182 n to 53.6 93.3 30.8 5.9 8.4 0.7 4.6 0.1 1.9 0.7 = - - 282 157 Portland, Ore....... Rapid City,' 8. D. Reno, Nev............ 92.9 45.2 56.0 6.1 51.6, 41.6 28.9 19.3 24.3 8.4 12.9 5.6 1.0 36 3.2 116 2.4 87 fi r |0 /i to 78.0 91.5 29.7 97.6 82.6 90.2 16.9 5.1 8.5 29.0 16.0 2.2 0.2 15.4 1.8 8.0 1.6 8.4 0.2 0.2 6.3 - 125 97 3.6 1.9 2.0 3.1 581 102 152 - - - - 154* Snow Melting Table 1 ....Data for determining Operating Characteristics of Snow-Melting Systems*' 1 (Conducted) 673 * From Air Conditioning, Heating and Ventilating, August, 1957, p. 87. > The period covered by this tebfe is from No. I to March 11, rm-< with February takes as a I8J4 day month. Total boors in period " 1830. * Tbe percentage is Colamas 2 and 3 pins the pement under hours of snowfall total 100 percent. Note that Hovn ofSa&cfaU does not include idling time, and is not actual operating time. See text. * Snowfalls of traceanwonta are not included; hence, Bonn/Saov/all indndesoaly tbcee hours of 0.01 inches irater equivalent per hoar snowfall. 'Out put does not indude allowance lor beck or edge losses since these depend on slab construction. Percentages total 100 percent at the number ol hours of snowfall, * #Wrw# Period is that during No Snowfall when the air temperature is S3 F or below. * When heatoutpot lor Ar -- 0 equals or exceeds the heat output for A, -- I, the heat transfer ci is ^on tbe air to the slab. This occurs when snowfall is at temperatures above 32 F. The sensible heat, q,, to raise the temperature of the snow to 32 F is where q, - 2.6s (32 - U) (3) a = rate of snowfall, inches of water equivalent per hour. f = air temperature, Fahrenheit. The heat of fusion, qm , to melt the snow is qm = 746s (4) The heat of evaporation, q,, (mass transfer) is 9. = AM0.0201P + O:055)(0.185 - pa,)Ar (5) where hjt -- heat of evaporation at the film temperature, Btu per pound. v = wind speed, miles per hour. Vn = vapor pressure of moist air, inches of mercury. The heat transfer, , (convection and radiation) is where 9 - 11.4(0.02010 + 0.055)(1/ - U)A, (6) 1/ = water film temperature, Fahrenheit. In addition to determining the four heating requirements, it is necessary to make allowance-for back and edge losses. These losses vary from 30 to 50 percent, depending upon the slab construction and fluid temperature. The equation for the required fluid temperature to provide an output q9 has been derived in Reference 2. For construc tion similar to.Fig. 1, the equation is i. - 0.5g* + f, , (7) where tm = mean fluid temperature (antifreeze solution), Fahrenheit. Equation 7 will apply to 1 in. as well as X in. IPS pipe-- see Fig. 1. Equations 2 to 7 permit the designer to determine the heating requirement of a snow-melting system. The solutions of these equations, however, require the simultaneous con sideration of the four climatic factors: (1) wind speed, (2) air temperature, (3) relative humidity, and (4) rate of snowfall. It is not satisfactory to use annual averages or mayimnms for the climatic factors. If averages or maximiims are used there is no assurance that they will ever occur simultaneously. It is necessary, therefore, to make a frequency analysis of the solutions to Equation 2 for all the occurrences of snowfall for a period of several years. Such an analysis for 33 cities appears in Table 1 which contains the operating information for a snow-melting system. For freesing temperatures (32 F and below) without snowfall the system may be idling which means that some heat is supplied to the slab so that there will be immediate malting when snow starts to fall. Column 4 of Table 1 gives the average temperature during freesing periods. This temperature is used in calculating .the idling load. The other term needed to calculate idling load is tbe wind speed during the period of,freezing temperatures. The column, Hours of Snowfall, indicates the. number of hours that snow is falling at rates equal to or greater than 0.01 in. of water equivalent per hour. There are snowfalls of